Process for producing alkyl nitrite

ABSTRACT

An alkyl nitrite is produced with high efficiency by bringing a nitrogen monoxide gas into contact with an aqueous solution of an alkyl alcohol and nitric acid in a reactor  2,  which aqueous solution may be a liquid fraction generated in an alkyl nitrite-production process in which an alkyl alcohol is reacted with nitrogen monoxide and oxygen in a reaction column  1.

TECHNICAL FIELD

The present invention relates to a process for producing an alkylnitrite from nitric acid, which may be a by-product of a process forproducing an alkyl nitrite from nitrogen monoxide, oxygen and an alkylalcohol, nitrogen monoxide, and an alkyl alcohol, with high efficiency.

The alkyl nitrite is useful as a material for producing other alkylesters, for example, dialkyl oxalate and dialkyl carbonate, throughoxidation processes.

BACKGROUND ART

As a process for producing an alkyl nitrite by reaction of an alkylalcohol with nitrogen monoxide and oxygen, Japanese Unexamined PatentPublication No. 11-189,570 and No. 6-298,706 disclose a process in whichan alkyl alcohol is fed into a top portion of a reaction column andallowed to fall from the top portion to the bottom portion through amiddle portion of the reaction column; separately, nitrogen monoxide andoxygen gasses are fed separately or together into the bottom portion ofthe reaction column and allowed to flow upward through the reactioncolumn and react with the falling alkyl alcohol to produce an alkylnitrite; and the resultant gas fraction containing the alkyl nitrite iscollected through an outlet located in the top portion of the reactioncolumn.

This process is however, unsatisfactory in that nitric acid is producedas a by-product, in a relatively large amount, and thus a large amountof the nitrogen materials for the process is in advantageously consumed.Therefore, it is desirable that the nitric acid is effectively utilizedto increase the efficiency of the production of the target alkylnitrite.

Japanese Unexamined Patent Publication No. 6-25,104 discloses a process,for continuously producing dimethyl carbonate from carbon monoxide andmethyl nitrite, in which nitrogen monoxide produced as a by-product isutilized to react with oxygen and methyl alcohol to regenerate methylnitrite and in this methyl nitrite-regeneration procedure, nitric acidis utilized as a nitrogen-supply source. In this process, nitric acid isthermally decomposed to generate nitrogen oxides. However, thedecomposition is carried out with an unsatisfactory efficiency and theeffective decomposition temperature is very limited. In this reactionsystem, nitric acid and nitrogen monoxide may contact methyl alcohol.However, the inventors of the present invention found that in thereaction system for producing methyl nitrite from nitrogen monoxide,oxygen and methyl alcohol, oxygen gas fed into the reaction systemcauses the concentrations of oxygen and nitrogen dioxide in the reactiongas to increase, and therefore, the production of methyl nitrite fromnitric acid, nitrogen monoxide and methyl alcohol with a high efficiencyis very difficult.

Also, Japanese Unexamined Patent Publication No. 11-189,570 discloses aprocess for producing an alkyl nitrite by withdrawing a liquid fractioncollected in a bottom portion of an alkyl nitrite regeneration reactioncolumn and containing nitric acid from the reaction column, and coolingand recycling the withdrawn liquid fraction through the reaction columnand a cooler. In connection with this reaction system, the inventors ofthe present invention found that while a contact of nitric acid and thealkyl alcohol with nitrogen monoxide occurs in the reaction system, thereaction system contains oxygen and nitrogen dioxide in increasedconcentrations due to the feed of oxygen into the reaction system and,therefore, the production of the alkyl nitrite from nitric acid,nitrogen monoxide and the alkyl alcohol with a high productionefficiency is very difficult.

Chemistry Letters, 1029 (1976) discloses that when nitrogen dioxide isproduced by a reaction of nitric acid with nitrogen monoxide as shown inreaction formula (1):NO+2HNO₃→3NO₂+H₂O  (1)in an initial stage of the reaction (1), a reaction shown in reactionformula (2) occurs.NO+HNO₃→NO₂+HNO₂  (2)

However, the reaction (2) is disadvantageous in that the equilibrium ofthe reaction (2) greatly deviates to the original system side, and thus,the production of nitrogen dioxide and nitrous acid in highconcentration is difficult and, when the equilibrium of the reaction (2)is moved to the resultant product system side, as the solubility ofnitrogen dioxide in water is relatively high and, in the reactionsystem, nitrogen dioxide, nitrous acid and nitric acid are equilibrateswith each other, an increase in the concentration of nitrogen dioxide orin the reaction pressure, causes the production of nitric acid toincrease and as a result, the production of nitrogen dioxide at a highconcentration becomes difficult. Due to the above-mentioneddisadvantages, the inventors of the present invention concluded that theabove-mentioned process is unsatisfactory as an industrial practice forproducing nitrogen dioxide and nitrous acid from nitric acid. Further,Encyclopaedia Chinrica, volume 1, 32nd Printing in Reduced Size, page665, discloses a process for producing nitrogen monoxide by reducing aconcentrated nitric acid with a bismuth, copper, led or mercury metal oriron oxide (II) or diarsenic trioxide. This process utilizes astoichiometric reaction and thus, the reducing material comprising theabove mentioned metal or oxide must be employed in a large amount.Therefore, the above-mentioned process is inadequate in industrialpractice.

SUMMARY OF THE INVENTION

The present invention intends to provide a process for producing analkyl nitrite from an alkyl alcohol, nitrogen monoxide and nitric acidwhich may be a by-product of a process for producing an alkyl nitritefrom an alkyl alcohol, nitrogen monoxide and oxygen, with a highefficiency and with a high industrial utilizability.

The process of the present invention for producing an alkyl nitritecomprises bringing a nitrogen monoxide gas into contact with an aqueoussolution of an alkyl alcohol and nitric acid, to produce an alkylnitrite.

In the process of the present invention for producing an alkyl nitrite,the alkyl alcohol preferably has 1 to 3 carbon atoms.

In the process of the present invention for producing an alkyl nitrite,the aqueous solution preferably contains nitric acid in a concentrationof 60% by mass or less.

In the process of the present invention for producing an alkyl nitrite,the aqueous solution preferably contains the alkyl alcohol in aconcentration of 5 to 70% by mass.

In the process of the present invention for producing an alkyl nitrite,the contacting of the nitrogen monoxide gas with the aqueous solution ofthe alkyl alcohol and nitric acid is preferably carried out at atemperature of from 0° C. to 200° C., under ambient atmospheric pressureor more but not more than 20 MPa G.

In the process of the present invention for producing an alkyl nitrite,the aqueous solution of the alkyl alcohol and nitric acid optionallyfurther contains a catalyst comprising at least one nitrate salt ofGroup VIII metals except for platinum group metals and of Group IBmetals of the Periodic Table.

In the process of the present invention for producing an alkyl nitrite,the catalyst is preferably present in an amount, in terms of metal, of20% by mass or less, based on the mass of the aqueous solutioncontaining the alkyl alcohol and nitric acid.

In the process of the present invention for producing an alkyl nitrite,the nitrogen monoxide gas is preferably substantially free from nitrogenoxides produced due to the presence of molecular oxygen contained in thenitrogen monoxide gas.

In the process of the present invention for producing an alkyl nitrite,the nitrogen monoxide gas is preferably substantially free from nitrogendioxide, dinitrogen trioxide, dinitrogen tetraoxide and molecularoxygen.

In an embodiment of the process of the present invention for producingan alkyl nitrite, (A) the aqueous solution of the alkyl alcohol andnitric acid is prepared in a reaction column by procedures such that thealkyl alcohol is fed into a top portion of the reaction column whileallowing the fed alkyl alcohol to fall down through the reactor column;nitrogen monoxide and oxygen gasses are fed separately or together intoa bottom portion of the reaction column while allowing the fed nitrogenmonoxide and oxygen gases to flow upward through the reaction column andto react with the falling alkyl alcohol; the resultant gas fractioncontaining alkyl nitrite gas is delivered through a top outlet of thereaction column and the resultant liquid fraction containing thenon-reacted alkyl alcohol and nitric acid dissolved in water iscollected in a bottom portion of the reaction column; and the collectedliquid fraction is withdrawn from the bottom portion of the reactioncolumn and a portion of the withdrawn liquid fraction is fed into areactor, and

(B) in the reactor, a nitrogen monoxide gas is brought into contact withthe fed liquid fraction, to produce an alkyl nitrite.

In the embodiment of the process of the present invention for producingan alkyl nitrite, preferably a gas fraction produced in the reactor andcontaining the alkyl nitrite is withdrawn from the reactor andintroduced into a portion located between the bottom and middle portionsof the reaction column, the introduced gas fraction is allowed to flowupward together with the gas fraction produced in the reactor columnthrough the reactor column and to be refined with the falling alkylalcohol, and the refined alkyl nitrite gas is delivered through the topoutlet of the reaction column.

In the embodiment of the process of the present invention for producingan alkyl nitrite, preferably, the nitrogen monoxide gas for the reactoris supplied from the same source as that for the reaction column.

In the embodiment of the process of the present invention for producingan alkyl nitrite, preferably, the portion of the liquid fraction fedfrom the bottom of the reaction column into the reactor contains nitricacid in a concentration of 20% by mass or less and the non-reacted alkylalcohol in a concentration of 15 to 60% by mass.

In the embodiment of the process of the present invention for producingan alkyl nitrite, preferably, another portion of the liquid fractionwithdrawn from the bottom portion of the reaction column is cooledthrough a cooler and recycled into middle portion of the reactioncolumn.

In the embodiment of the process of the present invention for producingan alkyl nitrite, preferably, the recycling procedures of the anotherportion of the liquid fraction from the bottom portion into the middleportion through the cooler is continuously carried out, while (a) therecycling rate, in terms of mass, of the another portion of the liquidfraction is controlled to 50 to 300 times the feed rate, in terms ofmass, of the alkyl alcohol into the reaction column;

(b) the total of the feed rate, in terms of mole, of the alkyl alcoholinto the reaction column and the recycling rate, in terms of mole, ofthe non-reacted alkyl alcohol contained in the recycled portion of theliquid fraction is controlled to 20 to 150 times the feed rate, in termsof mole, of whole nitrogen oxides into the reaction column, and

(c) the concentration of the non-reacted alkyl alcohol in the liquidfraction collected in the bottom portion of the reaction column iscontrolled to 15 to 60% by mass.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow sheet showing an embodiment of the process of thepresent invention for producing an alkyl nitrite,

FIG. 2 is a flow sheet showing another embodiment of the process of thepresent invention for producing an alkyl nitrite, and

FIG. 3 is a flow sheet showing a process for producing a dialkyloxalate, utilizing an embodiment of the process of the present inventionfor producing an alkyl nitrite.

BEST MODE OF CARRYING OUT THE INVENTION

In the process of the present invention, a nitrogen monoxide gas isbrought into contact with an aqueous solution of an alkyl alcohol andnitric acid while allowing nitric acid to react with nitrogen monoxideand the alkyl alcohol, to produce an alkyl nitrite.

In the aqueous solution, there is no limitation to the concentration ofnitric acid. Usually, nitric acid is preferably contained in aconcentration of 60% by mass or less, more preferably 1 to 60% by mass,more preferably 1 to 20% by mass, in the aqueous solution.

The alkyl alcohol usable for the process of the present inventionpreferably has 1 to 3 carbon atoms, and is more preferably selected frommethyl alcohol, ethyl alcohol n-propyl alcohol and isopropyl alcohol,still more preferably methyl alcohol.

In the aqueous solution, the alkyl alcohol is preferably contained in aconcentration of 5 to 70% by mass, more preferably 15 to 60% by mass,still more preferably 20 to 55% by mass.

The aqueous solution containing nitric acid and the alkyl alcohol may bea liquid fraction obtained, as a by-product, from a process in which analkyl alcohol is reacted with nitrogen monoxide and oxygen to produce analkyl nitrite, as disclosed in JP-11-189,570-A and JP-6-298,706-A. Inthis case, the aqueous solution (the liquid fraction) preferablycontains nitric acid in a concentration of 20% by mass or less, morepreferably 1 to 20% by mass, still more preferably 2 to 15% by mass, andthe non-reacted alkyl alcohol in a concentration of 15 to 60% by mass,more preferably 20 to 55% by mass.

The nitrogen monoxide gas usable for the process of the presentinvention, preferably contains nitrogen monoxide in a content of 4 to100% by volume. Usually, in the nitrogen monoxide gas, nitrogen monoxideis diluted with a dilute gas non-reactive with nitrogen monoxide, forexample, nitrogen gas. The nitrogen monoxide gas may contain a gascomponent which does not obstruct the alkyl nitrite-producing reactionfor the process of the present invention. Namely, the non-obstructivegas component may comprise carbon monoxide, carbon dioxide and alkylalcohol vapors. However, to produce the target alkyl nitrite from nitricacid with a high efficiency, the nitrogen monoxide gas is preferablysubstantially free from nitrogen oxides produced by the presence ofmolecular oxygen contained in the nitrogen monoxide gas. Namely, thenitrogen monoxide is preferably substantially free from nitrogendioxide, dinitrogen trioxide, dinitrogen tetraoxide and molecularoxygen. Also, the aqueous solution of the alkyl alcohol and nitric acidis more preferably free from the above-mentioned nitrogen oxides.

In the process of the present invention, nitrogen monoxide is preferablyfed in an amount of 1 to 50 moles, more preferably 1.5 to 20 moles,still more preferably 2 to 10 moles per mole of nitric acid into thereaction system.

In the process of the present invention, the reaction procedure ofnitric acid with nitrogen monoxide and the alkyl alcohol is preferablycarried out at a temperature of 0 to 200° C., more preferably 20 to 100°C. The reaction pressure is preferably the ambient atmospheric pressureor more, but not more than 20 MPa G, more preferably not more than 3 MPaG, still more preferably 0.2 to 1 MPa G. The reaction procedure of theprocess of the present invention can be carried out under pressurizedconditions as mentioned above.

In the process of the present invention, the reaction procedure ofnitric acid with nitrogen monoxide and the alkyl alcohol in an aqueousmedium is optionally carried out in the presence of a catalyst. Namely,the aqueous solution of nitric acid and the alkyl alcohol optionallyfurther contain a catalyst comprising at least one nitrate salt of GroupVIII metals, except for platinum group metals, and of Group IB metals ofthe Periodic Table. The nitrate salts of Group VIII metals for thecatalyst are preferably selected from, for example, ferric nitrate,nickel nitrate and cobalt nitrate. As a nitrate salt of Group IB metalsfor the catalyst, cupric nitrate is preferably employed. The catalyst ispreferably present in a content, in term of metal, of 20% by mass orless, more preferably 0.1 to 10% by mass, based on the total mass of theaqueous solution containing nitric acid and alkyl alcohol.

The reaction procedure of nitric acid with nitrogen monoxide and thealkyl alcohol is carried out in liquid phase in a batch type reactor ora continuous type reactor. The reaction procedure is conducted by thesteps of placing an aqueous solution containing nitric acid togetherwith an alkyl alcohol in a reaction vessel equipped with a stirrer; andintroducing a nitrogen monoxide gas into the aqueous solution under theambient atmospheric air pressure or higher, while stirring the aqueoussolution or blowing a nitrogen monoxide gas into the aqueous solutionunder a pressure higher than the ambient atmospheric pressure whilestirring the aqueous solution under the higher pressure. In thisprocedure, preferably substantially no nitrogen oxides are produced dueto the presence of molecular oxygen gas contained in the nitrogenmonoxide gas, thus are contained in the nitrogen monoxide gas, and arefed into the reaction system in the reactor. There is no specificlimitation to the reactor as long as the target reaction can be carriedout with satisfactory efficiency in the reactor and the reactor can havea single reaction section or a plurality of reaction sections or aplurality of reactors are connected to each other to constitute areaction system. The reactor may be in the form of a reaction vesselwith a stirrer, or a multistage type reaction column, for example, apacked reaction column or a sieve tray reaction column. However, as thereaction for the process of the present invention is of a gas-liquidcontact type, when the vessel type reactor equipped with a stirrer isused, the stirring apparatus is preferably provided with an impellercapable of dispersing gas bubbles in the aqueous solution with a highefficiency and a rotary means for the impeller capable of enhancing thegas-liquid contact efficiency; and when the multistage type reactorcolumn is used, the column preferably is packed with a packing materialcapable of enhancing the gas-liquid contact efficiency.

The resultant alkyl nitrite ester is delivered together with theabove-mentioned gas, as a gas fraction, from the reactor to the outsideof the reactor, and is optionally washed and refined and then suppliedto a desired use.

In an embodiment of the process of the present invention, the process ofthe present invention is utilized for a process for producing an alkylnitrite ester in which process, an alkyl alcohol is reacted withnitrogen monoxide and oxygen, to enhance the yield of the target alkylnitrite ester. In this case, nitric acid produced, as a by-product ofthe above-mentioned process, is utilized for the process of the presentinvention.

In this embodiment, (A) the aqueous solution of the alkyl alcohol andnitric acid is prepared in a reaction column by procedures such that thealkyl alcohol is fed into a top portion of the reaction column whileallowing the fed alkyl alcohol to fall down through the reactor column;nitrogen monoxide and oxygen gasses are fed separately or together intoa bottom portion of the reaction column while allowing the fed nitrogenmonoxide and oxygen gases to flow upward through the reaction column andto react with the falling alkyl alcohol; the resultant gas fractioncontaining alkyl nitrite gas is delivered through a top outlet of thereaction column and the resultant liquid fraction containing thenon-reacted alkyl alcohol and nitric acid dissolved in water iscollected in a bottom portion of the reaction column; and the collectedliquid fraction is withdrawn from the bottom portion of the reactioncolumn and a portion of the withdrawn liquid fraction is fed into areactor, and

(B) in the reactor, a nitrogen monoxide gas is brought into contact withthe fed liquid fraction, to produce an alkyl nitrite.

In the reactor, preferably, oxygen and nitrogen dioxide are not fed.

Preferably, a gas fraction produced in the reactor and containing thealkyl nitrite is withdrawn from the reactor and introduced into aportion located between the bottom and middle portions of the reactioncolumn, the introduced gas fraction is allowed to flow upward, togetherwith the gas fraction produced in the reactor column, through thereactor column and to be refined with the falling down alkyl alcohol,and the refined alkyl nitrite gas is delivered through the top outlet ofthe reaction column.

The embodiment of the process of the present invention will be furtherexplained with reference to the attached drawings.

Referring to FIG. 1, a reaction column 1 for producing an alkyl nitriteester has an upper section 1 a, a lower section 1 b, a bottom portion 1c located below the lower section 1 b, a top portion 1 d located abovethe upper section 1 a and a middle portion 1 e located between the upperand lower sections 1 a and 1 b, connected to each other. The reactioncolumn 1 is connected to a reactor 2 through a pipe line 3 through whichthe bottom portion 1 c of the reaction column 1 is connected to a middleportion 2 a of the reactor 2. The top portion 1 d of the reaction column1 is connected to a pipe line 4 connected to a supply source (not shownin FIG. 1) of a liquid alkyl alcohol. Also, the top portion 1 d isconnected to a pipe line 5 for withdrawing and optionally circulating agas fraction generated in the reaction column 1. The pipe line 5 has abranched pipe line 6 for discharging a portion of the gas fraction tothe outside of the reaction system.

The bottom portion 1 c of the reaction column 1 is connected at an upperpart thereof to a supply source (not shown) of nitrogen monoxide gasthrough a pipe line 7 and a supply source (not shown) of oxygen gasthrough a pipe line 7 a.

The pipe line 3 is connected at a middle part thereof to a pipe line 8having a cooler 9 located in a middle portion of the line 8 andconnected to the middle portion 1 e of the reaction column 1.

The reactor 2 has a pipe line 10 through which a top portion 2 b of thereactor 2 is connected to the pipe line 7, to feed a gas fractiongenerated in the reactor 2 into the upper part of the bottom portion 1 cof the reaction column 1. Also, a bottom portion 2 c of the reactor 2 isconnected to a supply source (not shown) of nitrogen monoxide gasthrough a pipe line 11. Further, the bottom of the reactor 2 isconnected to a pipe line 12 for withdrawing a liquid fraction generatedin the reactor 2.

Referring to FIG. 1, a liquid alkyl alcohol is fed into the top portion1 d of the reaction column 1 to allow the liquid alkyl alcohol to falldown through the upper and lower sections 1 a and 1 b of the reactioncolumn 1. Simultaneously, a nitrogen monoxide gas and an oxygen gas or anitrogen monoxide-oxygen mixed gas is fed into the upper part of thebottom portion 1 c through the pipe lines 7 and 7 a so that the fednitrogen monoxide and oxygen gasses flow upward through the reactioncolumn 1 and come into contact with and react with the falling liquidalkyl alcohol, to produce the alkyl nitrite in a gas phase. Theresultant gas fraction (a) containing the alkyl nitrite is washed orrefined with the falling alkyl alcohol and withdrawn from a top outletof the top portion 1 d of reaction column 1 through a pipe line 5. Also,the resultant liquid fraction containing non-reacted alkyl alcohol andnitric acid generated as a by-product of the above-mentioned reactionand dissolved in water, which is a by-product of the reaction, in thereaction column 1 is accumulated in the bottom portion 1 c of thereaction column 1. The liquid fraction (b) is withdrawn from the bottomportion 1 c and a portion (b-1) of the withdrawn liquid fraction (b) isfed into the middle portion 2 a of the reactor 2 through a pipe line 3,and another portion (b-2) of the withdrawn liquid fraction (b) isrecycled through the pipe line 8 and the cooler 9 into the middleportion 1 e of the reaction column 1. The cooled, and recycled liquidfraction (b-2) falls down together with the falling liquid alkyl alcoholthrough the lower section 1 b of the reaction column (1), to control thereaction temperature of the alkyl alcohol with nitrogen monoxide andoxygen to a desired level.

The portion (b-1) of the liquid fraction (b) fed into the reactor 2 isbrought into contact with the nitrogen monoxide gas fed into the bottomportion 2 c of the reactor 2 through the pipe line 11. Thus nitric acidcontained in the portion (b-1) of the liquid fraction (b) reacts withthe fed nitrogen monoxide and the non-reacted alkyl alcohol, to producean alkyl nitrite in a gas phase. A resultant gas fraction (c) containingthe target alkyl nitrite and the non-reacted nitrogen monoxide iswithdrawn from the top outlet of the top portion 2 b of the reactor 2through the pipe line 10 and fed into the upper part of the bottomportion 1 c of the reaction column 1 through the pipe line 7. The fedgas fraction (c) flows upward together with the nitrogen monoxide andoxygen gasses through the reaction column 1, and the non-reactednitrogen monoxide and oxygen in the gas fraction (c) reacts with thefalling alkyl alcohol and the resultant alkyl nitrite and the alkylnitrite in the gas fraction (c) are washed or refined with the fallingdown alkyl alcohol and delivered together with the gas fraction (a) fromthe reaction column 1 through the top portion 1 d through the pipe line5. The liquid fraction (d) accumulated in the bottom portion 2 c of thereactor 2 is optionally withdrawn through the pipe line 12.

Referring FIG. 2, the same reaction procedures as in FIG. 1 are carriedout, except that the gas fraction (c) generated in the reactor 2 iswithdrawn from the top outlet of the top portion 2 b of reactor 2through a pipe line 13 and fed into the middle portion 1 e of thereaction column 1.

In the above-mentioned embodiment of the process of the presentinvention, the nitrogen monoxide gas for the reactor 2 may be suppliedseparately from the nitrogen monoxide gas for the reaction column 1.However, preferably, the nitrogen monoxide gas is fed from a commonsupply source to both the reaction column 1 and the reactor 2. In thiscase, referring to FIGS. 1 and 2, the supply line of nitrogen monoxidegas from a common supply source (not shown) is preferably divided intoboth of the pipe line 7 connected to the reaction column 1 and the pipeline 11 connected to the reactor 2. The nitrogen monoxide gas ispreferably substantially free from nitrogen oxides produced due to thepresence of molecular oxygen in the nitrogen monoxide gas.

The gas fraction (c) generated in the reactor 2 and withdrawn from thetop portion 2 b of the reactor 2 is preferably fed into a portion of thereaction column 1 through which portion the liquid alkyl alcohol falls,more preferably a portion between the middle portion 1 e and the bottomportion 1 c of the reaction column 1. When the gas fraction (c)withdrawn from the reactor 2 is introduced into the middle portion 1 eof the reaction column 1 through the pipe line 13 shown in FIG. 2, theportion (b-2) of the liquid fraction withdrawn from the bottom portion 1c and cooled by the cooler 9 is preferably fed at a location below thelocation at which the gas fraction (c) from the reactor 2 is introducedinto the middle portion 1 e of the reaction column 1 through the pipeline 13, so that the gas fraction (c) fed into the reaction column canflow upward without contacting the liquid fraction (b-2) and can bewashed or refined with the falling alkyl alcohol in the upper portion 1a of the reaction column 1.

The nitrogen monoxide gas to be fed into the reaction column 1 maycontain nitrogen dioxide, dinitrogen trioxide and/or dinitrogentetraoxide. In this case, the content, in terms of gram atoms ofnitrogen, of nitrogen monoxide in the gas is more than 50% based on thetotal amount, in terms of gram atoms of nitrogen, of nitrogen monoxide,nitrogen dioxide, dinitrogen trioxide and dinitrogen tetraoxide.

The oxygen (molecular oxygen) is preferably employed in an amount of0.02 to 0.25 mole, more preferably 0.05 to 0.20 mole, per mole ofnitrogen monoxide, for the reaction in the reaction column 1.

For the reaction column 1, nitrogen monoxide and molecular oxygen areusually mixed with a gas non-reactive with the alkyl alcohol, oxygen,nitrogen monoxide and the reaction products in the reaction column 1,for example, nitrogen or carbon dioxide, and the mixed gas is fed, as amaterial gas into the bottom portion 1 c of the reaction column 1. Inthis case, the material gas preferably has a total content of nitrogenmonoxide and oxygen of 3 to 40% by volume, more preferably 5 to 20% byvolume, and a content of the non-reactive gas of 10 to 90% by volume,more preferably 20 to 80% by volume. The material gas for the reactioncolumn 1 may contain an alkyl alcohol in the state of a mist or vapor,in a content of 2 to 40% by volume, and further carbon monoxide and/oran alkyl nitrite.

The nitrogen monoxide gas may be mixed with the oxygen gas andoptionally a non-reactive gas in the above-mentioned mixing proportionsoutside the reaction column 1, and the resultant mixed gas is fed intothe reaction column 1. Alternatively, the nitrogen monoxide gas and theoxygen gas may be separately fed into an upper part of the bottomportion 1 c. In this case, the nitrogen monoxide gas for the reactioncolumn 1 is preferably supplied from a common supply source for thereactor 2.

The alkyl alcohol to be fed into the reaction column 1 is preferablyselected from alkyl alcohols having 1 to 3 carbon atoms, for example,methyl alcohol and ethyl alcohol and propyl alcohols, more preferablymethyl alcohol, and an alkyl nitrite is produced in response to thealkyl alcohol fed into the reaction column. The alkyl alcohol isoptionally cooled and preferably fed at a temperature of −15° C. to 50°C., more preferably −10° C. to 30° C.

As mentioned above, preferably, the alkyl alcohol is fed into a topportion of the reaction column and allowed to fall down through thereaction column, and the nitrogen monoxide gas and the molecular oxygengas are fed into a bottom portion of the reaction column and allowed toflow upward through the reaction column and to come into contact withthe falling alkyl alcohol. Thus, a gas-liquid contact reaction in acountercurrent relationship occurs in the reaction column.

The feed rate in terms of mole of the alkyl alcohol into the reactioncolumn is preferably 0.2 to 3.0 times, more preferably 0.3 to 2.0 timesthe total feed rate in terms of mole, of the nitrogen oxides includingnitrogen monoxide and another all nitrogen oxides produced from nitrogenmonoxide and oxygen in the material gas fed into the reaction column andnitrogen monoxide introduced from the reactor into the reaction column.Also, in the embodiment of the process of the present invention, aportion of the alkyl alcohol to be fed into the reaction column may befed in the state of a mist or vapor into the bottom portion of thereaction column through the pipe line for the nitrogen monoxide gas ornitrogen monoxide-oxygen mixed gas or through an other pipe line thanthe above-mentioned pipe line for the nitrogen monoxide gas or thenitrogen monoxide-oxygen mixed gas, while the composition of thematerial gas is maintained in the above-mentioned range.

In the reaction column, the reaction temperature of the alkyl alcoholwith nitrogen monoxide and oxygen is preferably controlled to 0 to 100°C., more preferably 5 to 80° C., still more preferably 10 to 60° C. Inthe embodiment of the process of the present invention, preferably, theliquid fraction accumulated in the bottom portion of the reaction columnis withdrawn by a liquid-transportation means, for example, a pump (notshown in FIGS. 1 and 2), a major portion of the withdrawn liquidfraction is introduced into a cooler to cool the liquid fraction to adesired temperature, the cooled liquid fraction is returned into aportion of the reaction column located between the middle portion andthe bottom portion of the reaction column, to allow the cooled liquidfraction to fall down. This liquid fraction-circulating procedure ispreferably carried out continuously, more preferably, continuously andsimultaneously with the above-mentioned reaction procedure of the alkylalcohol with nitrogen monoxide and oxygen. The withdrawn and cooledportion of the liquid fraction contributes to removing the reaction heatgenerated in the lower section and the bottom portion of the reactioncolumn and maintaining the reaction temperatures of the lower sectionwithin a desired range. The amount of the portion of the liquid fractionto be fed into the circulation system is established so that theabove-mentioned contribution can be attained.

In the liquid fraction-circulation procedure, (a) the circulation ratein terms of mass of the liquid fraction, in the other words, thereturning rate in terms of mass of the withdrawn liquid fraction intothe reaction column, is preferably controlled to 50 to 300 times, morepreferably 60 to 180 times, still more preferably 70 to 160 times, thefeed rate in terms of mass of the alkyl alcohol into the reactioncolumn; (b) a total feed rate in terms of mole of the alcohol fed intothe reaction column and the non-reacted alkyl alcohol contained in thereturned liquid fraction into the reaction column is preferablycontrolled to 20 to 150 times, more preferably 30 to 120 times, thetotal feed rate, in terms of mole, of whole the nitrogen oxides fed intothe reaction column; and (c) the concentration of non-reacted alkylalcohol contained in the liquid fraction collected in the bottom portionof the reaction column is preferably controlled to 15 to 60% by mass,more preferably 20 to 55% by mass.

In the circulation procedure, the portion of the withdrawn liquidfraction is preferably cooled to a temperature of 0 to 60° C. and 1 to20° C., more preferably 3 to 10° C. below the temperature of thewithdrawn liquid fraction before cooling. When the circulation procedureof the portion of the withdrawn liquid fraction from the reaction columnis carried out so that the above-mentioned requirements (a), (b) and (c)are satisfied, the reaction heat generated in the lower section 1 b canbe removed with high efficiency, the production of nitric acid can berestricted to a low level, and thus the above-mentioned gas-liquidcontact reaction can be effected with a high efficiency.

The above-mentioned feed rate of the alkyl alcohol into the reactioncolumn means a total feed rate of the alkyl alcohol fed in the states ofliquid and a vapor and/or mist from the outside into the reactioncolumn. For example, referring to FIGS. 1 and 2, the feed rate is of atotal of the liquid alkyl alcohol fed into the top portion 1 d of thereaction column 1 through the pipe line 4, the alkyl alcohol fed in thestate of a vapor or mist into the bottom portion 1 c of the reactioncolumn 1 through a pipe line 7, together with the nitrogen monoxide gas,and the alkyl alcohol contained in the gas fraction generated in thereactor 2 and fed into the reaction column 1 at a location between themiddle portion 1 e and the bottom portion 1 c thereof through the pipeline 10 or 13. However, the alkyl alcohol contained in the portion ofthe withdrawn liquid fraction and fed into the middle portion 1 e of thereaction column 1 through the pipe line 8 is not involved in thecalculation of the total feed rate of the alkyl alcohol into thereaction column 1.

The content in terms of mole of the alkyl alcohol in the liquid fractioncollected in the bottom portion 1 c of the reaction column 1 ispreferably 0.5 to 6.0 times, more preferably 1.0 to 5.0 times, the feedrate in terms of mole, of whole the nitrogen oxides fed into thereaction column 1.

Referring to FIGS. 1 and 2, the reaction column 1 necessarily has alower section 1 b in which the reaction (1) of the alkyl alcohol withnitrogen monoxide and oxygen is carried out and an upper section 1 a inwhich water produced as a by-product of the above-mentioned reaction(1), and contained, together with the alkyl nitrite, in the resultantgas fraction (a). Preferably, the upper section 1 a is connected to thelower section 1 b through a middle portion 1 e having an appropriatelength.

The upper portion 1 a is not limited to a specific type, as long as thealkyl alcohol can fall down through the upper section 1 a and thefalling down alkyl alcohol can absorb moisture contained in the gasfraction produced in the reaction column 1 and flowing upward throughthe upper section 1 a. For example, the upper section 1 a may have amultistage distillation column structure having a plurality of trays,for example, sieve trays or valve trays or a packed column structure inwhich packing materials, for example, Raschig rings or Pall rings, arepacked. There is no limitation to the structure and type of the lowersection 1 b as long as the reaction (1) of the alkyl alcohol withnitrogen monoxide and oxygen can be effected with a satisfactoryefficiency. For example, the lower section 1 b may have a multiple stagedistillation column structure or a packed column structure similar tothat of the upper section 1 a.

Namely, the reaction column 1 preferably has an upper section 1 a havinga multistage distillation column structure or a packed column structureand a lower section 1 b having a packed column structure and further amiddle portion 1 e formed between the upper and lower sections 1 a and 1b and having an appropriate length, the upper section 1 a, the middleportion 1 e and the lower section 1 b being connected with each other toform a body of reaction column, as shown in FIG. 1 or 2.

In the reaction apparatus shown in FIG. 1 or 2, preferably, the liquidfraction (b) accumulated in the bottom portion 1 c of the reactioncolumn 1 is continuously withdrawn through a pipe line 3, a minorportion (b-1) of the withdrawn liquid fraction (b) is continuously orperiodically introduced into a reactor 2 through a pipe line 3, and amajor portion (b-2) of the withdrawn liquid fraction (b) is continuouslycooled in the cooler 9 and returned into the middle portion 1 e of thereaction column 1 through the pipe line 8. In the reactor 2, nitric acidcontained as a by-product in the portion (b-2) of the liquid fraction(b) reacts with nitrogen monoxide fed through the pipe line 11 and withthe non-reacted alkyl alcohol in the portion (b-2), in accordance withthe process of the present invention. In this case, the feed rate of theliquid fraction (b) into the reactor 2 is preferably controlled so thatthe level of the liquid fraction accumulated in the bottom portion 1 cof the reaction column 1 is maintained constant.

The content of the non-reacted alkyl alcohol in the liquid fraction (b)is controlled as mentioned above, and thus the content of thenon-reacted alkyl alcohol contained in the portion (b-1) of thewithdrawn liquid fraction to be introduced into the reactor 2 ispreferably controlled to 15 to 60% by mass, more preferably 20 to 55% bymass. Also, the content of nitric acid contained in the portion (b-1) ofthe liquid fraction (b) is not specifically limited and may be 60% bymass or less. As it is preferred that the alkyl nitrite is produced witha high efficiency in the reaction column 1 by the circulation procedureof the withdrawn liquid fraction, the content of nitric acid in thewithdrawn liquid fraction (b) is preferably controlled to 20% by mass orless, more preferably 1 to 20% by mass, still more preferably 2 to 15%by mass. The withdrawn liquid fraction (b) of the reaction column 1contains water produced as a by-product of the reaction of the alkylalcohol with nitrogen monoxide and oxygen and a small amount of alkylnitrite.

In the reactor 2, a nitrogen monoxide gas is introduced into the liquidfraction (b-2) received in the reactor 2 through a pipe line 11 and thereaction of the nitric acid with nitrogen monoxide and the alkyl alcoholis carried out under the ambient atmospheric pressure or higher, whilestirring the liquid fraction. Alternatively, the nitrogen monoxide gasis introduced into the reactor 2 and the reaction is carried out underpressure above the ambient atmospheric pressure, while stirring theliquid fraction (b-2). In this reaction, preferably the nitrogenmonoxide gas and the liquid fraction fed into the reactor 2 aresubstantially free from nitrogen oxides produced due to the presence ofmolecular oxygen in the nitrogen monoxide gas. The reaction is carriedout in liquid phase and the reactor 2 may be of a batch type or acontinuous type.

The nitrogen monoxide to be fed into the reactor 2 may be a purenitrogen monoxide gas or a mixed gas in which nitrogen monoxide isdiluted with a non-reactive gas, for example, nitrogen gas or an inertgas. Preferably, the pipe line 11 for feeding the nitrogen monoxide gasinto the reactor 2 is connected to a pipe line 7 connected to a nitrogenmonoxide gas-supply source (not shown in FIGS. 1 and 2) at a locationupstream of a location at which the pipe line 7 a for feeding an oxygengas is connected to the pipe line 7, to prevent contamination, byoxygen, of the nitrogen monoxide gas to be fed into the reactor 2.

The molar amount of the nitrogen monoxide to be fed into the reactor 2must be equal to or more than the molar amount of nitric acid containedin the liquid fraction (b-1) in the reactor 2. In the case where thenitrogen monoxide gas fed into the reactor 2 is supplied from a commonsupply source for the nitrogen monoxide to be fed into the bottomportion 1 c of the reaction column 1, for example, where an alkylnitrite ester is produced while a large amount of nitrogen monoxide iscirculated through a production system in which the alkylnitrite-production system is combined with a dialkyl oxalate productionsystem, the feed rate of the nitrogen monoxide gas into the reactor 2 ispreferably controlled in such a range that the reaction of the alkylalcohol with nitrogen monoxide and oxygen in the reaction column and thereaction of the alkyl alcohol with nitrogen monoxide and nitric acid inthe reactor and other production procedures are not hindered. Where thenitrogen monoxide gas for the reactor 2 is supplied from a supply sourceother than that for the reaction column 1, the molar amount of the fednitrogen monoxide is 1 to 50 times the molar amount of nitric acidcontained in the liquid fraction introduced in the reactor 2.

In the reactor 2, the reaction temperature of nitric acid with nitrogenmonoxide and the alkyl alcohol is preferably 0 to 200° C., morepreferably 20 to 100° C., and the reaction pressure is preferably theambient atmospheric pressure or more but not more than 20 MPa G, morepreferably not more than 3 MPa G, still more preferably 0.2 to 1 MPa G.Namely, the reaction in the reactor 2 may be effected under pressure.

The reaction in the reactor 2 is optionally carried out in the presenceof a catalyst comprising at least one nitrate salt of Group VIII metalsexcept for platinum group metals and of Group IB metals of the PeriodicTable. The Group VIII metal nitrates are preferably selected from ferricnitrate, nickel nitrate and cobalt nitrate, and as a Group IB metalnitrate, cupric nitrate is preferably employed. The catalyst ispreferably present in a content, in terms of metal, of 20% by mass orless, more preferably 0.1 to 10% by mass, in the liquid fractioncontained in the reactor 2. The reactor 2 is not limited to a specificform or constitution, as long as the reaction of nitric acid withnitrogen monoxide and the alkyl alcohol can be effected with asatisfactory efficiency in the reactor 2.

The reactor 2 may have a single reaction space or a plurality ofreaction sections or may be constituted from a single reactor or aplurality of reactors connected with each other in series or inparallel. The reactor 2 may be in the form of a reaction vessel with astirrer, or a multistage reaction column, for example, a packed reactioncolumn or a sieve tray reaction column. As the reaction is a gas-liquidcontact reaction, when a stirrer-equipped reaction vessel is used as areactor 2, the stirring apparatus must be provided with an impeller anda rotary means capable of stirring the reaction system with a highstirring efficiency and a high gas-dispersing efficiency, and exhibit ahigh gas-liquid contact efficiency. When a multistage reaction column isused, a packing material having a high gas-liquid contact efficiency ispreferably packed therein.

In the reactor 2, the resultant gas fraction (c) containing the targetalkyl nitrite produced by the conversion of nitric acid is withdrawnthrough the top outlet 2 b of the reactor 2 and introduced into aportion of the reaction column 1 through which portion the alkyl alcoholfalls down, preferably which portion includes the middle portion 1 e,the lower section 1 b and the bottom portion 1 c of the reaction column1, through the pipe lines 10 and 7 of FIG. 1 or the pipe line 13 of FIG.2. In the case where the amount of the nitrogen monoxide gas introducedinto the reactor 2 is not too large, the gas fraction (c) is introducedinto either middle portion 1 e or the lower section 1 b of the reactioncolumn 1, preferably into the middle portion 1 e, more preferably at alocation of the middle portion 1 e above the location at which thecirculated portion (b-2) of the liquid fraction (b) is introduced intothe middle portion 1 c through the pipe line 8. In the case where thenitrogen monoxide is introduced in a large amount into the reactor 2,preferably, the gas fraction (c) containing the alkyl nitrite isdirectly introduced into an upper part of the bottom portion 1 c or intothe pipe line 7 at a location upstream to the location at which the pipeline 7 a for oxygen is connected to the pipe line 7 and downstream fromthe location at which the pipe line 11 for feeding nitrogen monoxide tothe reactor 2 is connected to the pipe line 7 as shown in FIG. 1, sothat the gas fraction (c) is mixed with the nitrogen monoxide gas andthen with the oxygen gas and the resultant mixed gas is introduced intothe bottom portion 1 c of the reaction column 1. The pipe line 7 ispreferably connected to an upper part of the bottom portion 1 c.

The reaction system shown in FIG. 1 or 2 is very useful for varioussynthesis reactions using carbon monoxide and an alkyl nitrite ester,for example, for a production of a dialkyl oxalate ester or a dialkylcarbonate ester. The reaction system enables the dialkyl oxalate esteror a dialkyl carbonate ester to be continuously produced with a highspace time yield and in a high selectivity, by a process shown in FIG.3.

In the process shown in FIG. 3, a reactor 21 for producing a dialkyloxalate ester (which will be referred to reactor 21 hereinafter) isconnected at an end portion thereof to a pipe line 22 for feeding acarbon monoxide gas into the reactor. Also, the reactor 21 is connectedto the pipe line 5 for delivering the gas fraction containing an alkylnitrite from the top portion 1 d of the reaction column 1. Further thereactor 21 is connected at another end portion thereof to a pipe line 23for withdrawing a gas fraction (e) generated in the reactor 21. The pipeline 23 is connected to a lower portion of an absorption column 24connected at an upper portion thereof to a pipe line 24 for feeding anabsorption liquid comprising a liquid alkyl alcohol. The absorptioncolumn 24 is connected at a bottom portion thereof to a pipe line 25 forwithdrawing a liquid fraction generated in the absorption column 24. Thetop portion of the absorption column 24 is connected to the pipe line 7.In the reactor 21, a platinum group metal catalyst is contained.

Referring to FIG. 3, the gas fraction (a) generated in the reactioncolumn 1 and containing an alkyl nitrite is fed into the reactor 21through the pipe line 5 and a carbon monoxide gas is fed into thereactor 21 through the pipe line 22. In the reactor 21, carbon monoxidereacts with the alkyl nitrite in the presence of a platinum group metalcatalyst, to produce a dialkyl oxalate ester. The resultant gas fractioncontaining the dialkyl oxalate ester is withdrawn from the reactor 21and fed into the bottom portion of the absorption column 24 through thepipe line 23. The fed gas fraction (e) is allowed to flow upward throughthe absorption column 24. An absorption liquid comprising a liquid alkylalcohol is fed into the upper portion of the absorption column 24 andallowed to fall down through the absorption column 24. The flowing gasfraction (e) comes into contact with the falling absorption liquid incountercurrent relationship, to allow the dialkyl oxalate ester to beextracted and concentrated in the absorption liquid. The resultantliquid fraction (f) comprising the dialkyl oxalate ester extracted inthe absorption liquid is withdrawn from the absorption column 24 throughthe pipe line 25 and subjected to a procedure for isolating the targetdialkyl oxalate ester from the absorption liquid by using a distillationcolumn (not shown in FIG. 3).

Also, a resultant gas fraction (g) generated in the absorption column 24and containing nitrogen monoxide produced as a by-product of thereaction carried out in the reactor 21, non-reacted carbon monoxide, thealkyl alcohol vapor, and non-reactive dilution gas, is withdrawn fromthe top portion of the absorption column 24 and fed, as a nitrogenmonoxide-containing material gas, into the bottom portion 1 c of thereaction column 1 through the pipe line 7, together with the oxygen gasfed through the pipe line 7 a. In this case, the reaction column 1serves as an alkyl nitrite-regeneration column.

Referring to FIG. 3, an alkyl alcohol is fed into the top portion 1 d ofthe reaction column 1 through a pipe line 4 and falls down through thereaction column 1. The material gas containing nitrogen monoxide andoxygen and fed into the bottom portion 1 c of the reaction column 1 flowupward through the reaction column 1 and comes into contact with thefalling alkyl alcohol in a countercurrent relationship and a gas-liquidreaction is carried out to regenerate an alkyl nitrite. The resultantgas fraction (a) containing the alkyl nitrite is withdrawn from the topportion 1 d of the reaction column 1 and introduced into the reactor 21through the pipe line 5. Optionally, a portion of the withdrawn gasfraction (a) is discharged through a pipe line 6.

The resultant liquid fraction (b) containing the non-reacted alkylalcohol and nitric acid produced as a by-product is accumulated in thebottom portion 1 c of the reaction column 1 and continuously withdrawnfrom the bottom portion 1 c through a pipe line 3. A portion of thewithdrawn liquid fraction is circulated through a cooler 9 and a pipeline 8 and returned into the middle portion 1 e of the reaction column 1and the remaining portion of the withdrawn liquid fraction (b) is fedinto the upper portion 2 a of the reactor 2 and brought into a reactionwith nitrogen monoxide gas fed into the bottom portion 2 c of thereactor 2 through the pipe line 11. The reaction of nitric acid withnitrogen monoxide and the alkyl alcohol in the rector 2 is preferablycarried out while feeding a nitrogen monoxide gas substantially freefrom nitrogen oxides produced due to the presence of molecular oxygencontained in the nitrogen monoxide gas. The resultant gas fraction (c)containing an alkyl nitrite is withdrawn through the top outlet of thereactor 2 and fed into the bottom portion 1 c or middle portion 1 e ofthe reaction column 2 through which portion the alkyl alcohol fallsdown, through the pipe lines 10 and 7 or the pipe line 13. The withdrawngas fraction (c) may be directly fed into the bottom portion 1 c of thereaction column 1. The fed gas fraction (c) is washed or refined by thefalling alkyl alcohol and withdrawn, together with the gas fraction (a)from the reaction column 1 and fed into the reactor 21 through the pipeline 5. In this case, the nitric acid produced, as a by-product, in thereaction column 1 can be utilized as a component for producing an alkylnitrite in the reactor 2, with a high efficiency and can reduce the lossof nitrogen component due to a discharge of the liquid fraction (b)containing nitric acid and/or the gas fraction (a) containing an alkylnitrite and nitrogen monoxide. Thus, the amount of the nitrogencomponent to be supplemented into the reaction system can be decreasedby the above-mentioned simple specific reaction system.

EXAMPLES

The process of the present invention will be further illustrated indetail by the following examples.

In the examples and comparative examples, the content of nitric acid isdetermined by an ion chromatography and a titration and the contents ofanother compounds are determined by a gas chromatography.

Example 1

An autoclave made from SUS 316, having a capacity of one liter andequipped with a stirrer having four paddle type impeller, a gas-supplynozzle a gas-withdrawing nozzle, and a liquid-withdrawing nozzle ischarged with 540 g of a 16.7 mass % aqueous nitric acid solution and 230g of methyl alcohol and air in the autoclave was replaced by nitrogengas, and the inside of the autoclave was pressurized with nitrogen gasto a pressure of 0.4 MPa G. Then, a mixed gas of 10% by volume ofnitrogen monoxide with nitrogen was fed into the autoclave at a feedrate of 16 N liter/hour through the gas feed nozzle while the reactionsystem is stirred, a portion of the gas fraction in the autoclave iswithdrawn through the gas-withdrawing nozzle so that the pressure of thereaction system in the autoclave constant, and the temperature of thereaction system is increased to 50° C.

One hour after the stage at which the temperature of the reaction systemreached 50° C., the composition of the gas fraction withdrawn at a flowrate of 19.2 N liter/hour from the autoclave was measured. As a result,the withdrawn gas fraction comprised 11.2% by volume of methyl nitrite,2.1% by volume of nitrogen monoxide, 8.9% by volume of methyl alcohol,2.8% by volume of water and 75% by volume of nitrogen. Further, 3 hoursafter the reaction temperature reached 50° C., the concentration ofnitric acid in the liquid fraction contained in the autoclave wasmeasured. As a result, the concentration of nitric acid was 9.5% by massand thus the conversion rate of nitric acid was about 2 g/hour.

The results are shown in Table 1.

Examples 2 to 7

In each of Examples 2 to 7, the same procedures as in Example 1 werecarried out except that the reaction temperature and pressure and thestirring conditions were changed as shown in Table 1, and in Example 7,the aqueous nitric acid solution was added with 0.2 mole/liter of acatalyst consisting of cupric nitrate. The results are shown in Table 1.

Comparative Example 1

The same procedures as in Example 1 were carried out, except that theaqueous nitric acid solution was replaced by 770 g of a 11.7 mass %aqueous nitric acid solution and no methyl alcohol was mixed into theaqueous nitric acid solution. One hour after the reaction temperaturereached 50° C., the gas fraction withdrawn from the autoclave throughthe gas-withdrawing nozzle at a flow rate of 16.4 N liter/hr wassubjected to an analysis. The gas fraction comprised 9.5% by volume ofnitrogen monoxide, 0.5% by volume of nitrogen dioxide, 2.8% by volume ofwater and 8.72% by volume of nitrogen. No conversion of nitric acidduring the reaction procedure was recognized.

TABLE 1 Conversion Reaction conditions Flow rate of MN rate of Stirringmixed gas concentration nitric Pressure Temperature speed (*)₁ (*)₂ acid(MPa G) (° C.) (rpm) (N liter/hr) (% by volume) (gHNO₃/hr) Example 1 0.450 1100 16 11.2 2 2 0.4 50 1100 60 10.5 6 3 0.4 27 1100 60 11.2 7 4 0.450 1100 180 9.7 16 5 0.4 50 2100 300 11.0 31 6 0.2 28 1100 16 6.0 1 70.2 28 1100 16 6.0 1 [Note] (*)₁A mixed gas of 10% by volume of nitrogenmonoxide with nitrogen (*)₂Concentration of methyl nitrite in thewithdrawn gas fraction

Example 8

A reaction system as shown in FIG. 1 was employed. A reaction column 1had an inside diameter of 158 mm and a height of 1400 mm and comprisedan upper section 1 a extending downward from a location of 50 mm below atop of the column at a length of 800 mm and packed with 100 mm Raschigrings and a lower section 1 b extending downward from a location of 30mm below the bottom end of the upper section 1 a at a length of 400 mmand packed with 10 mm Raschig rings.

In to the reaction column 1, a material gas comprising 6.4% by volume ofmethyl nitrite, 12.6% by volume of nitrogen monoxide, 11.5% by volume ofcarbon monoxide, 4.8% by volume of methyl alcohol and 64.7% by volume ofnitrogen was fed at a feed rate of 15.0 Nm³/hr under a pressure of 0.32MPa G (3.2 kg/cm² G) into an upper part of a bottom portion 1 c througha pipe line 7; an oxygen gas was fed at a feed rate of 0.33 Nm³/hr intothe bottom portion 1 c through a pipe lines 7 a and 7; and methylalcohol was fed at a temperature of 20° C. at a feed rate of 3.5liters/hr into a top portion 1 d of the reaction column 1 through a pipeline 4.

The pressure in the reaction column 1 was controlled to 0.3 MPa G (3.0kg/cm² G) by using a valve placed in the pipe line 5.

A resultant liquid fraction (b) accumulated in the bottom portion 1 c ofthe reaction column 1 was withdrawn through a pipe line 3. A majorportion (b-2) of the withdrawn liquid fraction was introduced into acooler 9 by using a pump (not shown in FIG. 1) placed in the pipe line 8and cooled. The cooled portion (b-2) of the liquid fraction was returnedat a flow rate of 360 liters/hr into the middle portion 1 e of thereaction column. The cooler 9 was operated so that the temperature ofthe liquid fraction in the bottom portion 1 c of the reaction column 1can be adjusted to 40° C., by flowing a cooling water having atemperature of 5° C. through a cooling jacket (not shown in FIG. 1) ofthe cooler 9. After the reaction reached stable conditions, a gasfraction (a) comprising 14.72% by volume of methyl nitrite, 4.01% byvolume of nitrogen monoxide, 11.54% by volume of carbon monoxide, 4.82%by volume of methyl alcohol, 64.92% by volume of nitrogen was deliveredfrom the top portion 1 d of the reaction column 1 through a pipe line 5at a total flow rate of 14.95 Nm²/hr.

Also, the liquid fraction comprised 57.4% by mass of methyl alcohol,33.6% by mass of water, 8.6% by mass of nitric acid, and 0.5% by mass ofmethyl nitrite and was withdrawn at a flow rate of 1.75 liters/hrthrough the pipe line 3.

A 10 liter capacity autoclave reactor 2 made of SuS 316 was employed.The reactor 2 was equipped with two steps of disc turbines and a levelmeter and a stirrer, and connected to a pipe line 11 connected to anitrogen monoxide supply source (not shown in FIG. 1), a pipe line 12for discharging a liquid fraction (d) generated in the reactor 2 fromthe bottom portion 2 c, the pipe line 3 through which a middle portion 2a of the reactor 2 is connected to the bottom of the reaction column 1,and a pipe line 10 through which the top portion 2 b of the reactor 2 isconnected to the pipe line 7 at a location upstream to the connection ofthe oxygen-feeding pipe line 7 a and downstream from the connection ofthe nitrogen monoxide feeding pipe line 11 to the pipe line 7.

Into the reactor 2, a portion of the withdrawn liquid fraction from thereaction column 2 was fed in an amount of 6 liters through the pipe line3, air in the inside of the reactor 2 was replaced by nitrogen gas, andthe inside of the reactor 2 was pressurized with the nitrogen gas to apressure of 0.3 MPa G (3 kg/cm² G). Then the nitrogen monoxide gas (thematerial gas) is introduced at a feed rate of 2 Nm³/hr into the liquidfraction (b) in the reactor 2 through the pipe line 11, while the liquidfraction (b) in the reactor 2 was stirred at a stirring rate of 600 rpm,the temperature of the reaction system was increased to 50° C., and aresultant gas fraction is withdrawn through the pipe line 10 so that thepressure of the reaction system in the reactor 2 is maintained at theabove-mentioned level. Simultaneously, a portion (b-1) of the withdrawnliquid fraction (b) from the reaction column 1 was introduced at a feedrate of 1.75 liters/hr into the reactor 2 through the pipe line 3. Also,a resultant liquid fraction (d) generated in the reactor 2 was withdrawnat a flow rate of 1.61 liters/hr through the pipe line 12 so that thereaction temperature was maintained constant at 50° C. and the liquidlevel of the reaction system is maintained constant at a liquid volumeof about 0.8 liter.

The withdrawn liquid fraction (d) had a composition of 58.0% by mass ofmethyl alcohol, 37.4% by mass of water, 3.7% by mass of nitric acid and0.4% by mass of methyl nitrite. In the reaction in the reactor 2, theconversion of nitric acid was 60.4% by mass. Also, the withdrawn gasfraction (c) had a composition of 9.42% by volume of methyl nitrite,10.03% by volume of carbon dioxide, 11.36% by volume of carbon monoxide,4.74% by volume of methyl alcohol and 63.93% by volume of nitrogen, andwas introduced at a flow rate of 2 Nm³/hr into the reaction column 1through the pipe lines 10 and 7.

After the reaction conditions in the reaction column 1 and the reactor 2became stable, the composition of the gas fraction (a) delivered fromthe reaction column 1 through the pipe line 5, was subjected to the gasanalysis. It was confirmed that the gas fraction (a) comprised 15.56% byvolume of methyl nitrite, 3.59% by volume of nitrogen monoxide, 11.50%by volume of carbon monoxide and 4.79% by volume of methyl alcohol and64.56% by volume of nitrogen and was delivered at a total flow rate of15.04 Nm³/hr.

Example 9

The same reaction procedures as in Example 8 were carried out exceptthat the reaction temperature in the autoclave reactor 2 was changedfrom 50° C. to 70° C.

After the temperature and liquid level in the autoclave reactor 2 becamestable, the liquid fraction (d) was withdrawn from the reactor 2 at aflow rate of 1.61 liters/hr, had contents of methyl alcohol of 58.3% bymass, water of 39.2% by mass, nitric acid of 1.90% by mass and methylnitrite of 0.4% by mass and exhibited a conversion of nitric acid of79.6%.

Also, the gas fraction (c) was withdrawn from the reactor 2 andintroduced at a flow rate of 2.1 Nm³/hr into the reaction column 1through the pipe lines 10 and 7. The withdrawn gas fraction comprised11.15% by volume of methyl nitrite, 8.86% by volume of nitrogenmonoxide, 10.98% by volume of carbon monoxide, 7.21% by volume of methylalcohol and 61.79% by volume of nitrogen.

Further, after the reactions in the reaction column 1 and the autoclavereactor 2 became stable, the gas fraction (a) withdrawn from the topportion 1 d of the reaction column 1 through the pipe line 5 wassubjected to an analysis. It was confirmed that the gas fraction (a)comprised 15.69% by volume of methyl nitrite, 3.29% by volume ofnitrogen monoxide, 11.39% by volume of carbon monoxide, 5.72% by volumeof methyl alcohol and 63.92% by volume of nitrogen and was withdrawn ata total flow rate of 15.19 Nm³/hr.

Comparative Example 2

The same reaction procedures as in Example 8 were carried out exceptthat all the procedures relating to the autoclave reactor 2, including,for example, the introduction of the liquid fraction (b) from thereaction column 1 and the feed of the nitrogen monoxide gas and thereaction in the reactor 2, were omitted.

It was confirmed that the nitric acid produced as a by-product by thereaction in the reaction column 1 was not utilized to produce the targetmethyl nitrite, and thus the yield of the methyl nitrite could not beincreased.

INDUSTRIAL APPLICABILITY

The process of the present invention enables an alkyl nitrite to beindustrially produced with high efficiency, from nitric acid, nitrogenmonoxide and an alkyl alcohol. In the process of the present invention,nitric acid produced as a by-product of a process for the production ofan alkyl nitrite from an alkyl alcohol, nitrogen monoxide and oxygen canbe utilized to enhance the yield of the target alkyl nitrite. Also, inthe process of the present invention, an aqueous solution of nitric acidin a relatively low concentration and an alkyl alcohol can be used toproduce the target alkyl nitrite with high efficiency.

The process of the present invention is very useful for a syntheticreaction using as material compounds, an alkyl nitrite ester and carbonmonoxide, for example, a production of dialkyl oxalate ester or dialkylcarbonate ester. In this synthetic process, the process of the presentinvention contributes to decreasing the loss of nitrogen components suchas nitric acid due to the discharge of the liquid fraction and as alkylnitrite and nitrogen monoxide, due to the discharge of the gas fraction,generated by the reaction of an alkyl alcohol with nitrogen monoxide andoxygen, and saving the supplementation of the nitrogen components.

1. A process for producing an alkyl nitrite comprising bringing anitrogen monoxide gas into contact with an aqueous solution of an alkylalcohol and nitric acid, to produce an alkyl nitrite.
 2. The process forproducing an alkyl nitrite as claimed in claim 1, wherein the alkylalcohol has 1 to 3 carbon atoms.
 3. The process for producing an alkylnitrite as claimed in claim 1, wherein the aqueous solution containsnitric acid in a concentration of 60% by mass or less.
 4. The processfor producing an alkyl nitrite as claimed in claim 1, wherein theaqueous solution contains the alkyl alcohol in a concentration of 5 to70% by mass.
 5. The process for producing an alkyl nitrite as claimed inclaim 1, wherein the contact of the nitrogen monoxide gas with theaqueous solution of the alkyl alcohol and nitric acid is carried out ata temperature of from 0° C. to 200° C., under an ambient atmosphericpressure or more but not more than 20 MPa G.
 6. The process forproducing an alkyl nitrite as claimed in claim 1, wherein the aqueoussolution of the alkyl alcohol and nitric acid further contains acatalyst comprises at least one nitrate salt of Group VIII metals exceptfor platinum group metals and of Group IB metals of the Periodic Table.7. The process for producing an alkyl nitrite as claimed in claim 6,wherein the catalyst is present in an amount, in terms of metal, of 20%by mass or less, based on the mass of the aqueous solution containingthe alkyl alcohol and nitric acid.
 8. The process for producing an alkylnitrite as claimed in claim 1, wherein the nitrogen monoxide gas issubstantially free from nitrogen oxides produced due to the presence ofmolecular oxygen in the nitrogen monoxide gas.